416 
MILK. 
It is the fat or butter of milk that imparts its characteristic 
white, opaque appearance. The fat occurs in a multitude 
of little globules, which, distributed throughout the sub¬ 
stance of the fluid, gives rise to its peculiar white colour. 
The fat-globules being slightly lighter than the fluid in 
which they float, slowly rise to the surface on standing, 
and form a layer, more or less thick, which we call the 
cream. By suitable means the whole of the fat-globules 
can be removed, and a transparent liquid obtained, which 
contains all the other constituents of the milk. It is 
often supposed that the cream is the essential part of the 
milk, and we hear of its being given to children in the belief 
that it is a kind of concentrated milk of superior nutritive 
value. This, however, is not the case; cream is only rich in 
fatty substances, and its use in our system is much the same 
as is performed by the fat of meat. Indeed, we may say that 
cream or the butter is to milk what fat is to meat—viz., that 
portion which furnishes respiratory material. We may, how¬ 
ever, regard it as a superior and more highly organized kind 
of fat, since it approaches more nearly to the kind of fat- 
occurring in our own bodies. The market prices of new and 
skim milk are quite disproportionate to the relative nutritive 
value; since the latter, having lost nothing but its cream (a 
material for which other substances could be easily sub¬ 
stituted) is but little inferior in point of feeding qualities to 
new milk; and where, as in many country districts, skim 
milk, of better quality than that frequently supplied in towns 
as new, can be had for a halfpenny a quart, a more extended 
use of it amongst poor persons would be greatly to their 
advantage. In milk from which the cream has been removed, 
the other constituents may be separated as follows: On the 
addition of a few drops of hydrochloric acid, or of vinegar, the 
caseine, or cheesy matter, separates in flocculent masses. 
When this is removed by straining, we have left in solution 
the sugar and the greatest part of the mineral salts, which 
may be obtained by evaporating, or boiling off the liquid in 
a water bath until it dries up. The caseine is, perhaps, the 
most interesting of the above-named constituents of milk. 
Caseine is one of the group of plastic elements already 
spoken of as the flesh-forming materials of food. It resembles 
very closely, in its chemical properties, the gluten of grain, 
or the fibrine of flesh. We have also mentioned the close 
relation that exists between the caseine of milk and the 
vegetable caseine of peas, beans, and other leguminous pro¬ 
ducts. The mineral elements of milk are exceedingly rich 
in phosphoric acid, a substance especially necessary in the 
